Michael Anthony is honoring the short life of his infant grandson by joining an upcoming fundraising walk for Children's Hospital Los Angeles.

The former Van Halen bassist shared the news of his devastating personal loss on Facebook, posting an update informing fans that his grandson Rex had died at just 15 days old. Diagnosed with heart disease shortly after his birth, Rex underwent open heart surgery to correct his condition, but doctors soon realized he was too weak to recover from the procedure.

"After watching him decline to a condition we understood he could not return, we decided to hold him in our arms while life support (ecmo) was removed," reads the post. "We are tremendously proud of Rex. In the short time on earth he left a lasting impression that our family will cherish. We really appreciate the outstanding support from friends and family and the incredible staff at Children's Hospital who did everything possible to save Rex's life."

In honor of those efforts — and Rex's too-brief time on Earth — Anthony has joined this year's Walk L.A. fundraiser, scheduled for June 17 at Griffith Park in Los Angeles. Noting that the non-profit organization is "the only hospital solely dedicated to the health of children in Los Angeles," Anthony's seeking to raise $3,450 for his Walk L.A. team, dubbed Rex and the Heart Beaters.

Saying he's doing the walk to "give back a little to the hospital that did so much for my grandson and other children that come here," Anthony is also inviting fans to start their own Walk L.A. fundraising pages and take part in the event, which takes participants on a 4-km loop through the park. For more information, visit the Walk L.A. website.